1. Field of the Invention
This invention relates generally to forward looking infrared (FLIR) systems and more particularly to a FLIR system utilized for both navigation and target acquisition/tracking.
2. Description of the Prior Art
Forward looking infrared (FLIR) systems are generally known, particularly as it relates to their use in connection with military aircraft which have the requirement of flying at low altitudes and acquiring targets at night for the purpose of delivering armorment or ordnance against them. Current state of the art systems generally require two separate and distinct infrared sensing systems which alternately operate in either/or operating modes, i.e. only one mode at a time. One system has a wide field of view that develops an IR picture looking ahead of the aircraft in order to present information to a pilot for the purposes of flying the aircraft in what is referred to as a pilotage mode. This system is known as the navigation FLIR. Additionally, a separate FLIR system is located on the aircraft for implementing what is referred to as the targeting function which comprises acquisition and tracking of a target and is known as the targeting FLIR. The second system has a narrow field of view that has magnification or telescopic properties such as a zoom capability so that targets can be located. The targeting FLIR system normally produces a high magnification visual image that enables the pilot to survey for the target and acquire the target in time to maneuver his aircraft for attack and weapon delivery.
The state of the art has, moreover, developed from locating the pilotage and targeting FLIR systems in pods mounted beneath the aircraft to an internally mounted system including a single small optical turret protruding from the aircraft. Such a system includes a single optical gimbal assembly providing a single line of sight which includes two aligned fields of view, a wide field of view used for pilotage purposes, and a narrow field of view utilized for limited targeting. With such a system coupled to a helmet mounted sight and display (HMS/D) unit, it provides a pilot with the ability to look in all forward directions for his navigation or pilotage purpose and it also provides him with an optical zoom to give a relatively smaller or narrower magnified field of view of a potential target so that the pilot can look down and observe the target by manually switching from the wide pilotage field of view to the narrower targeting field of view. However, there are inherent limitations in such an optical system where there is only one gimbal and one line of sight because it is impossible for such a system to simultaneously provide two separate images along separate lines of sight, such as where the pilot needs to control one line of sight which is slaved to his head in order to fly the aircraft, and the other line of sight needs to search for and acquire a target which is located at a bearing that is generally offset from the longitudinal axis of the aircraft and pilot's line of sight.
Accordingly, it can readily be seen that switching back and forth between pilotage and targeting modes in a single line of sight system can impair the pilot's situational awareness where, in addition to flying the aircraft under relatively difficult conditions, e.g. close to the ground, he must turn his head not only to find the target, but must also often update the tracking of the target once acquired. Therefore, it offers a low probability of his performing a successful mission, which, in addition to flying the aircraft, is to seek out and destroy a target in a first pass attack sequence.